"Cotten, it turns out, was a serial operator of “exit scams: Ponzis that, after reaching a critical volume, abruptly close up shop.” He ran his first pyramid scheme at age 15. Cotten and his partner in Quadriga, Michael Patryn—an alias!—met on a message board for Ponzi schemers, where they bonded by running Ponzi schemes on each other"
I'm well aware of the multitude of scams, hacks, etc. involving [centralized] cryptocurrency exchanges, but it doesn't actually have much to do with blockchain technologies itself, at least not in the context being discussed here.
If you give over control to cryptocurrency by sending your cryptocurrency to some entity that exists outside of a trust-less blockchain system (centralized exchange or otherwise) then that entity can do whatever they want with it (technically-speaking), and you are essentially then reverting back to and relying on non-blockchain technologies at that point (The exchange was probably just a typical web app built with some common web framework and RDBMS). Obviously, ponzi schemes are possible without blockchain technologies and in a purely blockchain world, because of the transparency of transactions, it would be very difficult to pull off without having willing-participants.
There is a separate discussion to be had of how to use blockchain with "legacy" centralized systems and how to make it user-friendly for non-experts, but it's not an actual problem with blockchain technologies itself, but more of a second-order problem.
The main thing being discussed was digital assets, so if you have 2 pure digital assets that are compatible with smart contracts, you can exchange without any trust and it prevents things like ponzi schemes. Government money, like in the example, really is more of a "legacy" centralized system, which allows for this. That's partly why you are seeing entities like Coinbase try to create "stable" cryptocurrencies [1] that try to mirror the value of government money.
"you are essentially then reverting back to and relying on non-blockchain technologies at that point"
Yes, my point is that's not a choice. It's like making the "choice" to fall down after you free yourself from the shackles of the "conventional crutch system".
Clearly this is not an actual problem with walking without crutches - millions of people handle walking that way all the time!
"Cotten, it turns out, was a serial operator of “exit scams: Ponzis that, after reaching a critical volume, abruptly close up shop.” He ran his first pyramid scheme at age 15. Cotten and his partner in Quadriga, Michael Patryn—an alias!—met on a message board for Ponzi schemers, where they bonded by running Ponzi schemes on each other"